1. Field of the Invention
The present invention relates to a digital switching system, and more particularly to a technique for controlling a fixed rate connection such as a CBR (Constant Bit Rate) connection, etc. within a cell switching system such as an ATM (Asynchronous Transfer Mode) system, etc.
2. Description of the Related Art
A data transfer based on an ATM method has been made practical as a way of realizing a B-ISDN (Broadband-Integrated Service Digital Network). The B-ISDN handles data used by computers and services such as telephony speech signals, facsimile signals, VOD (Video On Demand) signals, etc. within a single network.
To support these various services, a CBR service for securing a fixed bandwidth and services such as rt-VBR, nrt-VBR, ABR, UBR, etc. whose bandwidths in use (simply referred to as bandwidths hereinafter) change depending on the use state of the network, are provided. These services are provided in order to be adaptable to different upper applications depending on use purposes.
Among the above described services, a CBR service is intended to handle an upper application service such as telephony speech, VOD, etc., which requires a strict delay condition.
An ATM exchange occupies a physical bandwidth corresponding to a requested bandwidth when establishing a CBR service connection.
FIG. 1 shows the configuration of a conventional ATM switching system.
When a subscriber telephone 2, terminal 3, or television (TV) 4, which is to receive a VOD (Video On Demand) service, originates a call, a CAC (Connection Admission Control) unit 9 within a node 1, which is an ATM exchange that receives the signal via a subscriber line 5, 6, or 7, checks whether or not there is an empty band of a CBR connection to a destination by referencing a bandwidth table 10. If there is an empty band, the CAC unit 9 establishes a connection.
For the services (such as rt-VBR, nrt-VBR, ABR, and UBR) whose bandwidths change depending on cell traffic, the node 1 controls their cell traffic and performs statistical multiplexing control. Therefore, a line efficiency is high and subscribers are not troubled so much.
However, because the CBR service occupies a bandwidth based on a PCR (Peak Cell Rate), the subscriber TV 4 which receives a CBR service occupies a particular bandwidth resource possessed by the node 1. Accordingly, the subscriber telephone 2 or terminal 3, which handles another application, can perform statistical multiplexing only with the remaining bandwidth resource except for the bandwidth occupied by the CBR service.
Conventionally, the CBR service could not accept a subscriber who requests a physical bandwidth exceeding a total bandwidth allocated to the CBR service.
With the above described conventional technique, no special restriction is imposed when an ATM exchange establishes a CBR connection. Namely, if the physical bandwidth used by the CBR connection permits, any large number of CBR connections can be set up. Therefore, the CBR service which handles an application service with a strict delay condition such as a VOD service, a speech service, etc. occupies the bandwidth of a switch within an ATM exchange, which leads to the connection disability of a subscriber using a different application service (such as an Internet service).
As a result, the number of CBR service subscribers must be restricted so as to overcome the above described problems. In this case, however, cost per subscriber cannot be reduced.
The present invention was developed in the above described background, and aims at effectively using the bandwidth of a switch within an exchange, and at preventing each service subscriber from being troubled, when a cell exchange such as an ATM exchange, etc. establishes a fixed rate connection.
The present invention assumes an ATM switching device (an ATM exchange) for switching fixed-length cells (ATM cells), and for controlling a fixed rate connection (CBR connection).
A fixed rate bandwidth setting unit (bandwidth table 20) sets fixed rate bandwidth (CBR bandwidth) information being the information about the bandwidth that a fixed rate connection can occupy.
A use state setting unit (use state 22) sets fixed rate used bandwidth information (bandwidth used by a CBR service) being the information about the bandwidth that a fixed rate connection currently uses.
A call controlling unit (CAC unit 19) controls whether or not to permit the establishment of a fixed rate connection while performing an overbooking bandwidth control which permits the bandwidth indicated by fixed rate used bandwidth information to exceed the bandwidth indicated by fixed rate bandwidth information, based on the fixed rate bandwidth information set in the fixed rate bandwidth setting unit and on the fixed rate used bandwidth information set in the use state setting unit, when establishing the fixed rate connection, and updates the fixed rate used bandwidth information set in the use state setting unit.
The above described configuration according to the present invention can be implemented so that the fixed rate bandwidth setting unit and the use state setting unit are arranged for a corresponding capability part such as a line device (line unit 30) for switching or concentration-multiplexing cells, a shelf device (shelf unit 31) for concentrating the line device, a switching device (switching unit 32) for switching cells input/output to/from the shelf device, etc., and the call controlling unit controls the overbooking bandwidth control for the corresponding capability part while referencing the fixed rate bandwidth setting unit and the use state setting unit, which are arranged for the corresponding capability part.
The configuration according to the present invention described so far can be implemented so that the call controlling unit attempts to broaden the bandwidth that a fixed rate connection can occupy, if the bandwidth that the fixed rate connection currently uses covers the bandwidth that the fixed rate connection can occupy, when performing the overbooking bandwidth control; changes the fixed rate bandwidth information set in the fixed rate bandwidth setting unit according to the broadened bandwidth; and controls whether or not to permit the establishment of the fixed rate connection.
In this case, the call controlling unit can be configured to attempt to broaden the bandwidth that the fixed rate connection can occupy based on the bandwidth information of the fixed rate connection, which is notified from an adjacent cell switching device, if the bandwidth that the fixed rate connection currently uses covers the bandwidth that the fixed rate connection can occupy, when performing the overbooking bandwidth control; and notifies the adjacent cell switching device of the new bandwidth information about the fixed rate connection according to the control result. In this case, the communication of the above described bandwidth information is made between the cell switching devices, for example, by using a resource management cell or a signaling message.
Or, the call controlling unit can be configured to attempt to broaden the bandwidth that a fixed rate connection can occupy based on the state of the bandwidth of the fixed rate connection controlled in other capability units within the cell switching device, if the bandwidth that the fixed rate connection currently uses covers the bandwidth that the fixed rate connection can occupy, when performing the overbooking bandwidth control.
The configuration according to the present invention described so far can be implemented so that the fixed rate bandwidth information set in the fixed rate bandwidth setting unit is changed according to a use rate change of the fixed rate connection, which depends on a time zone, or an increase/decrease in a requested number of fixed rate connections.
The configuration according to the present invention described so far can be implemented so that each of cell switching devices for exchanging a signaling message regarding a fixed rate connection adds the information for specifying whether or not the fixed rate connection is overbooking-bandwidth-controlled by the call controlling unit, to the signaling message regarding the fixed rate connection, which is exchanged by each of the cell switching devices.
The configuration according to the present invention described so far can be implemented so that the call controlling unit performs the overbooking bandwidth control only for the connection from a server to a client when a fixed rate connection of a server-client type is established.
Another configuration of the present invention assumes a method for controlling a fixed rate connection (CBR connection) which implements a communication using fixed-length cells (ATM cells).
First of all, a virtual path connection is established between a cell switching device and a user home device when a fixed rate connection is established.
When the fixed rate connection is established for the terminal accommodated by the user home device, whether or not to permit the establishment of the fixed rate connection is controlled while performing the overbooking bandwidth control which permits the bandwidth that the fixed rate connection currently uses to exceed the bandwidth of the virtual path connection.
According to the present invention, a multiplexing effect can be obtained for a CBR connection, etc. without troubling any other users, by performing an overbooking bandwidth control for a fixed rate connection such as a CBR connection, etc. As a result, the use efficiency of a line can be improved for the CBR connection, etc.
Additionally, according to the present invention, traffic control with more flexibility and a higher accuracy can be performed for a CBR connection, etc. by performing an overbooking bandwidth control for a fixed rate connection such as a CBR connection, etc. for the corresponding capability part within a cell switching device.
At this time, the capability units in which the overbooking bandwidth control is performed are restricted, so that an efficient traffic control can be performed.
Furthermore, according to the present invention, a line use efficiency can be improved within an entire network by obtaining the bandwidth information about an adjacent capability unit or an adjacent node CBR connection, etc., and by attempting to broaden an available bandwidth of the CBR connection, etc. based on the obtained information.
In this case, the bandwidth information of the fixed rate connection such as a CBR connection, etc. can be efficiently exchanged between adjacent cell switching devices by using a resource management cell or a signaling message.
Still further, according to the present invention, a line use efficiency can be further improved by changing an available bandwidth of a fixed rate connection such as a CBR connection, etc. according to a time zone.
Still further, according to the present invention, a priority for determining whether or not to secure a dedicated bandwidth can be assigned to a fixed rate connection by adding to a signaling message the information for specifying the presence/absence of an overbooking bandwidth control, when the signaling message regarding the fixed rate connection is exchanged between cell switching devices.
Still further, according to the present invention, a line use efficiency on a server side can be improved without degrading the communication quality of a service request issued from a client side to the server side by performing an overbooking bandwidth control only for the connection from the server side to the client side when a fixed rate connection of a server-client type is established.
Still further, according to the present invention, a limited line resource of a fixed rate connection connected by a user can be effectively shared among terminals by performing an overbooking bandwidth control for the fixed rate connection within a user home device.